We need to set the cell image to none explicitly if the item doesn't have any,
otherwise the image for the previous cell would be reused.
Closes#14112.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70941 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775